1. Field of the Invention
The present invention relates to a microchip useful as a μ-TAS (Micro Total Analysis System) or the like that is suitably used for such purposes as biochemical tests for DNA, protein, cell, immunity, and blood for example, chemical synthesis and environmental analysis. More specifically, the present invention relates to a microchip having therein a fluid retaining reservoir for containing a fluid such as reagent to be mixed or reacted with a sample to be tested or analyzed for example.
2. Description of the Background Art
In recent years, in the fields of medical care, health, food, and drug discovery for example, sensing, detection or quantitation of biological substances such as DNA (Deoxyribo Nucleic Acid), enzyme, antigen, antibody, protein, virus, and cell as well as chemical substances has become increasingly important, and various biochips and micro chemical chips (they are hereinafter referred to collectively as microchip) with which the above-described substances can be easily and conveniently measured have been proposed. The microchip can be used to allow a series of experimental and analytical operations usually performed in a laboratory to be conducted within the chip of several centimeters per side and approximately several millimeters to one centimeter in thickness. The microchip accordingly provides many advantages that the amounts of samples and reagents to be used are very small, the cost is low, the reaction rate is high, high throughput test can be conducted, and the test results can be immediately obtained at the site where the sample was taken, for example. The microchip is suitably used for biochemical tests such as blood test for example.
The microchip commonly includes therein “fluid circuit” that is a fluid channel network constituted of portions (chambers) where a specific treatment is performed on a fluid, and a fine fluid channel appropriately connecting these portions. In the test and analysis of a sample (such as blood or a specific component of the blood for example in the case of the blood test) by means of a microchip having therein such a fluid circuit as described above, the fluid circuit is used to perform various fluid treatments such as measurement of a sample introduced into the fluid circuit, measurement of a reagent to be mixed with the sample, and mixing of the sample with the reagent. The various fluid treatments can be performed by applying a centrifugal force in an appropriate direction to the microchip.
A microchip having a fluid circuit in which a reagent to be mixed or reacted with a sample or a specific component in the sample is contained and retained in advance, namely so-called reagent-contained microchip, has been known (see for example Japanese Patent Laying-Open No. 2007-017342, U.S. Pat. No. 4,883,763 and Japanese Patent Laying-Open No. 2007-229631). The reagent-contained microchip usually includes, as a part of the fluid circuit of the microchip, one or a plurality of reagent retaining reservoirs for retaining a reagent. Further, the reagent-contained microchip usually has a reagent inlet formed in one of the surfaces of the microchip and extending through to the reagent retaining reservoir for injecting a reagent into the reagent retaining reservoir. The reagent-contained microchip is produced in the following manner. A reagent is injected through the reagent inlet, and thereafter a sealing label (seal) or the like for example is bonded to the surface of the microchip to seal the reagent inlet. The microchip is shipped in this state for use.
Regarding such a reagent-contained microchip, in order to perform a test and analysis for a sample with high precision, degradation of the contained reagent has to be sufficiently suppressed or prevented from the time when the microchip is produced (when the reagent is injected) to the time when the microchip is actually used. Further, the reagent should be sufficiently suppressed or prevented from flowing out of the reagent retaining reservoir, which could be caused for example by impact on the microchip or by an increase of the internal pressure of the reagent retaining reservoir during transportation and delivery of the microchip for example. This is for the following reason. If the reagent deteriorates or flows out of the reagent retaining reservoir, the reagent and the sample (or a specific component contained in the sample) will not properly react, or the microchip contains no reagent to be mixed with the sample (or a specific component contained in the sample) when the sample is tested and analyzed, or the reagent and the sample (or a specific component contained in the sample) are not mixed at an appropriate ratio, which could result in the possibility that accurate and highly reliable test and analysis results cannot be obtained.
U.S. Pat. No. 4,883,763 and Japanese Patent Laying-Open No. 2007-139480 for example each disclose a reagent-contained microchip in which a reagent contained in the microchip is sealed so that deterioration of the reagent and unintended outflow of the reagent can be prevented until the microchip is used. FIG. 21 is a plan view showing an example of the reagent-contained microchip disclosed in U.S. Pat. No. 4,883,763. In the microchip shown in FIG. 21, chambers 96 and 98 retaining a reagent are sealed containers slidable with respect to a substrate and each having an openable portion 10 where an opening can be made. At respective positions opposite to chambers 96 and 98, spike or needle-shaped opening means 12 are provided. This structure allows the reagent to be sealed in chambers 96 and 98 until the microchip is used. When the microchip is used, this structure allows the reagent to flow out through an opening made in openable portion 10 by opening means 12 as a result of application of a centrifugal force in F0 direction shown in FIG. 21.
Although the above-described structure is highly effective at preventing deterioration of the reagent and unintended outflow of the reagent, there is a possibility that the whole amount of the reagent does not flow out from the hole made by opening means 12. If some of the reagent remains in chamber 96 or 98, application of a centrifugal force in a subsequent fluid treatment process could cause the remaining reagent to flow out again to adversely affect mixing or reaction of the reagent with a sample or adversely affect the results of the test and analysis of a fluid mixture of a sample and the reagent.
Further, the microchip disclosed in U.S. Pat. No. 4,883,763 has a problem that the structure of the reagent retaining reservoir (chamber) is very complicated and thus the reservoir is not easy to produce. Specifically, it is necessary to provide a window in the container in which the reagent is sealed and further attach a film or the like to the window so that a hole can be formed with a needle or the like, as openable portion 10. It is also necessary to slidably dispose the container on the substrate. Further, since the microchip has a movable portion (slidable container), the microchip lacks operational stability. For example, when an operational failure of the movable portion occurs, the reagent may not flow out.
Japanese Patent Laying-Open No. 2007-229631 discloses a microreactor in which a liquid such as reagent or sample can be surely stopped at a desired position and the liquid can be surely restarted from the position where the liquid is stopped. The disclosed microreactor includes a water repellant valve constituted of an upstream side connection hole having a smaller cross-sectional area than the cross-sectional area of an upstream side flow channel, a downstream side connection hole having a smaller cross sectional area than the cross-sectional area of a downstream side flow channel, and a connection hole communicating portion allowing communication between the upstream side connection hole and the downstream side connection hole and having a continuously varying cross-sectional area. On the two opposing ends of a storage portion where a reagent or sample is stored, the water repellant valves are provided respectively (see in particular FIGS. 3 and 5 of Japanese Patent Laying-Open No. 2007-229631).
Even if the water repellant valve having the above-described structure is provided, impact or an increase of the internal pressure for example during transportation and delivery of the microchip could cause the liquid to move from a predetermined position or flow out. Thus, there still has been room for improvement of the ability to retain a fluid such as reagent (ability to prevent outflow or leakage of the fluid).